The invention relates, generally, to ink jet printers and, more particularly, to an improved print head ink temperature control device.
The prior art systems include drop-on-demand and continuous jet systems. In many cases, such systems use specially formulated inks for quick drying, clear marking and other characteristics which are desired by the user. These inks are temperature sensitive and therefore variation in ambient temperatures, such as in factories where products to be marked are being manufactured, adversely affect printing. Ink jet printing systems frequently locate the electronics and ink supplies remotely from the point where products are to be marked by the ink drops. The ink jet printhead including the nozzle is located at the point of marking and may be connected to a cabinet by a relatively long (xc2xd to thirty foot) umbilical-like tube which supplies both ink and electrical control signals to the printhead assembly.
It is somewhat difficult to maintain the ink at the optimum temperatures desired for best printing. For example, many ink jet systems are rated for use in environments within the temperature range of 40xc2x0 and 120xc2x0 Fahrenheit. Many inks, however, optimally operate within a temperature range of as little as plus or minus five degrees. For example, an ink formulated for use at 75xc2x0 is desirably maintained between 70xc2x0 and 80xc2x0 F. during printing operations. For this reason, control of the temperature of ink used in ink jet printing systems are known to be beneficial.
U.S. Pat. No. 5,623,292 is assigned to the instant assignee and discloses a temperature controller for an ink jet printer. However, the temperature controller requires a temperature sensor and a control circuit. The temperature sensor and control circuit are potential failure items and increase the cost and manufacturing complexity.
Japanese Published Patent Application JP 04336256A discloses a positive temperature coefficient (PTC) heater used to heat ink in channels of a printhead. However, the design is somewhat complicated in that a plurality of PTC heaters are used and each PTC heater has an electrode on opposing sides of the heater. Japanese Published Patent Application JP 58053176A discloses a PTC thermistor for heating fluids and which has mutually isolated side electrodes to permit bi-directional current flow.
The use of PTC thermistor""s are also shown in, for example, U.S. Pat. Nos. 5,015,986, 5,086,308 and 5,784,089 and Japanese Published Application JP 04345852A.
It is desired to provide a printhead of an ink jet printer having a heater which can maintain ink temperature within a predetermined, acceptable range of temperatures.
It is further desired to provide such a printhead heater which maintains the temperature of ink in the multiple channels or chambers at a uniform temperature.
It is further desired to provide an ink heater which compensates for a printhead having some ink channels which dissipate heat at a rate different than the other ink channels.
It is still a further feature of the invention to provide a printhead having an ink heater which is less costly to manufacture and has an improved life span.
The present invention provides an ink jet print head, comprising, a plurality of ink channels disposed in a common plane, each of said channels having at least one orifice for projecting ink towards a substrate, and an ink heater made of a thermistor material, the ink heater having a substantially planar configuration and extending in a plane parallel to the plane of the channels and adjacent thereto.
The present invention also provides an ink jet print head comprising, a top body portion, an intermediate body having an upper side and a lower side, a plurality of ink channels disposed in a common plane along the upper side, each of said channels having at least one orifice for projecting ink towards a substrate, the upper side of the intermediate body portion located adjacent the top body portion, a main body portion located adjacent the lower side of the intermediate body portion, and an ink heater of a thermistor material, the ink heater having a substantially planar configuration and is located between the lower side of the intermediate body portion and the main body portion, and extends in a plane parallel to the plane of the channels and adjacent thereto.
In a preferred embodiment, the ink heater is designed to compensate for an ink jet print head having certain ink channels which dissipate heat at a higher rate than other ink channels. In particular, the ink heater includes electrodes formed on the PTC thermistor material in an arrangement or pattern which compensates for the varying heat dissipation of the ink channels.